Interplay between confinement,

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Interplay between confinement, turbulence and
magnetic topology
Nils P. Basse, S. Zoletnik1, W. L. Rowan2 et
al. MIT Plasma Science and Fusion
Center 1KFKI-RMKI, Euratom Association, Budapest,
Hungary 2Fusion Research Center, University of
Texas at Austin
This idea originates from density fluctuation
studies of Wendelstein 7-AS plasmas with a
small-angle scattering diagnostic.
C-Mod Monday Meeting, 22nd of March 2004
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W7-AS density fluctuations
Wavenumber is 15 cm-1 Dotted line is good
confinement (q_a 2.9) Solid line is bad
confinement (q_a 2.75)
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EFIT equilibrium 1040319018
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Waveforms shot 1040319018
Scorecard 9 full length plasmas, 6 early
disruptions, 1 fizzle. We had 7 no power shots
(cycle and engineering tests, computer and CAMAC
problems). We also had breaker faults and
transmitter D was lost in shot 7.
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PCI fluctuations, central channel
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Reflectometry fluctuations, 132 GHz
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Preliminary conclusions

• Always takes some shots to obtain density control
  for these inner wall limited L-mode discharges.
• Initial analysis of density fluctuation autopower
  spectra shows that no discernable change is
  observed as q_a is lowered from 2.9 to 2.75.
• Correlations between various turbulent fields,
  e.g. magnetic and density fluctuations, may
  display some differences. Analysis to be done.
• Temperature profiles still need to be checked so
  far no clear development has been found.
• If additional experiments are made, I suggest to
  make a density scan in Ohmic plasmas. The
  transition was quite sensitive to density in
  W7-AS High density lead to a large transition.